Since it is simple to handle a photoreactive composition, the photoreactive composition is widely used for printing plate materials, various resists and ultraviolet curable coating materials.
As the photoreactive composition, a composition of a photopolymerizable monomer and/or a photopolymerizable polymer and an aryl diazonium salt (see Patent Document 1) and a photoreactive composition containing a photoacid generator such as a triaryl sulfonium complex salt added therein (see Patent Document 2) have hitherto been known.
However, when these photoacid generators such as an aryl diazonium salt and a triaryl sulfonium complex salt are used, since the maximum absorption wavelength is 300 nm or less, there was a problem that a reaction rate of the photoreactive composition is insufficient under the conditions where a light source in the near ultraviolet range of about 300 to 400 nm is used.
The present inventors have intensively studied so as to solve such a problem of the prior art and fond that a specific compound shows high sensitivity in the near ultraviolet range, thus proposing a photopolymerization initiator using the compound and a photocurable composition containing the same (see Patent Document 3).    Patent Document 1: Specification of U.S. Pat. No. 3,205,157    Patent Document 2: Specification of U.S. Pat. No. 4,231,951    Patent Document 3: Japanese Unexamined Patent Publication (Kokai) No. 2004-189720